This invention relates to a process for the preparation of certain p-nitroso-diphenylhydroxylamines.
It is known that p-nitroso-diphenylhydroxylamines may be obtained through the dimerizing rearrangement of nitrosobenzenes in concentrated sulphuric acid, E. Bamberger et al., Ber. 31 p. 1513 (1898). As such a process is strongly exothermic, relatively large quantities of concentrated sulphuric acid have been utilized to obtain adequate mixing and dissipation of heat. To separate the reaction product, ice, or water, must be added to the mixture. Large quantities of dilute sulphuric acid accumulating thereby are neutralized and subsequently discharged as waste water, as reclamation of the sulphuric acid, is not economically justifiable, especially due to its contamination with nitrogen-containing organic materials. As a consequence, the foregoing process is not suitable for industrial-scale preparation of p-nitroso-hydroxylamines.
German patent application disclosure No. 2,020,043 teaches that the dimerizing rearrangement of the nitrosobenzenes may be performed with a sulphuric acid of at least 50% by weight, preferably at least 75% by weight, in the presence of an organic liquid, such as an aliphatic hydrocarbon, a halogen hydrocarbon, or an aromatic nitro compound, at a temperature of 5.degree. to 50.degree. C. Since, at the elevated temperatures, the reaction product decmposes very quickly in the strongly acidic solution, it is necessary to remove the heat of reaction quickly, and this is accomplished by the organic liquid. However, in such a process, as well, sulphuric acid is utilized in a large excess, namely, up to 10 times, preferably 2.5 to 6.5 times the molar quantity of nitrosobenzene. Thus, the previously discussed disadvantages of the process according to Bamberger et al. are also encountered in the process of the German patent application. Aside from the foregoing, the quality of the reaction product is not totally acceptable. In addition to products sulfonated in the nucleus, the products also contain considerable quantities of other constituents. When stoichiometric quantities of sulphuric acid are utilized, the p-nitroso-diphenylhydroxylamine is obtained in the form of its sulfate, as a tough, dark mass, technically hard to handle, which, in addition to products sulfonated in the nucleus, also contains substantial quantities of tar.
In German Pat. No. 1,147,237, a process is disclosed which utilizes hydrogen fluoride as a dimerizing agent, rather than concentrated sulphuric acid. The rearrangement takes place at a temperature between -20.degree. C. and 50.degree. C., if necessary in the presence of an inert organic solvent, K. Wiechert et al., Z. Chem. 15 (1975), p. 21. In the foregoing process, as well, the dimerizing agent is utilized in great excess, because the hydrogen fluoride serves not only as a catalyst, but also as a solvent. When the hydrogen fluoride is utilized in stoichiometric quantities, one obtains the yield of only 25%, of theoretical. In addition, the product is contaminated with products fluorinated in the nucleus. After the reaction, the hydrogen fluoride may be distilled off under a vacuum and may be recirculated. However, hydrogen fluoride has a low boiling point, an extremely penetrating odor, and, when inhaled, its vapors are very poisonous. Aside from the foregoing, the desired product is obtained as a viscous mass, which is still contaminated with 10 to 20% of adhering hydrogen fluoride. It is practically impossible to reclaim the adhering hydrogen fluoride, since, under the conditions required to accomplish the same, the p-nitroso-diphenylhydroxylammonium fluorides decompose into a brownish-black mass. Thus, the wash water is also contaminated with hydrogen fluoride. Furthermore, there are corrosion problems associated with such a process. Execution of the process therefore requires high expenditures for equipment, so that such a process, as well, is not very suitable for industrial-scale preparation of p-nitroso-diphenylhydroxylamines.
Furthermore, it is known that in the treatment of nitrosobenzene with peroxytrifluoroacetic acid, p-nitrosodiphenylhydroxylamine will be formed in addition to nitrobenzene, J. H. Boyer, J. Org. Chem. 24 (1959), p. 2038. Thus, the peroxytrifluoroacetic acid, on the one hand, oxidizes the nitrosobenzene to nitrobenzene, and on the other hand, it catalyzes the dimerization of the nitrosobenzene to p-nitrosodiphenylhydroxylamine. At higher temperatures it favors the formation of nitrobenzene, and at lower temperatures, that of p-nitroso-diphenylhydroxylamine. In the most favorable case, one obtains 35% of theoretical, of p-nitroso-diphenylhydroxylamine, and thus such a process is not very selective and likewise is not very well suited for the industrial-scale preparation of p-nitroso-diphenylhydroxylamines.
The primary object of the present invention is therefore to provide a process for the preparation of p-nitroso-diphenylhydroxylamines, which may be utilized in an industrialscale operation.